Separable contacts for vacuum circuit interrupters with asymmetric weld-breaking contact configurations

ABSTRACT

A vacuum-type circuit interrupter is provided having separable contacts with an asymmetric arrangement, or configuration, which will aid in breaking welds by accomplishing a tearing, or blending action upon the separable contacts at the initial time of contact separation during the opening operation.

United States Patent [72] Inventor Richard L. Hundstad [56] ReferencesCited Pittsburgh, Pa UNITED STATES PATENTS P 2 2 3.036, 1 s0 5/1962Greenwood 200 144 .2 5253 6,19" 3,174,019 3/1965 Jansson 200 144 .2

9 Assignee w house Elecmc Corpomfion 3,327,081 I 6/1967 Pflanz 200/144(.2) Pittsburgh, Pa. FOREIGN PATENTS 914,146 7/1949 Germany ZOO/144(2)54 SEPARABLE CONTACTS FOR VACUUM CIRCUIT f 'V Schaefe INTERRUPTERS WITHASYMMETRIC WELD Assistant Examiner-Robert A. Vanderhye BREAKNG CONTACTCONFIGURATIONS AttorneysA. T. Stratton, C. L. McHale and W. R. Crout 5Claims, 2 Drawing Figs. [52] US. Cl...., 200/ 144, ABSTRACT: Avacuum-type circuit interrupter is provided 200/166 having separablecontacts with an asymmetric arrangement, 51 Int. Cl ..H0lh 33/66, orconfi uration, which will aid in breaking welds b accoml g y HOlh 1/12plishing a tearing, or blending action upon the separable con- [50]Field of Search 200/ 144.2, tacts at the initial time of contactseparation during the open- 165,166 B, 67 PK; 21C/3509 ing operation.

PATENTED JUL 6197i FIG.I.

i gw la y ZZZZZHZ ZZZZ ZZZ INVENTOR Richard L. Hundstod AII'TORNEYdglINESSES a BACKGROUND OF THE INVENTION The present invention concernsa concept in the design of separable contacts, or electrodes for vacuuminterrupters. Specifically, it is the intent of the present invention tosuggest a geometrical arrangement of contact or electrode components,which will reduce the severity of the problem of electrode welding.

Contact materials presently being used in vacuum interrupters weld whenbrought together under high-voltage conditions. The high voltage causesprestrike followed by arcing, melting, and finally welding when thecontacts are forced together. The magnitude of the force required tobreak the weld, so that the contacts can be opened depends upon manyfactors including the arc voltage, the current, the contact area, whichis melted, and surely the most important-the material itself.

Certain investigators have obtained patents on low-weldstrength contactmaterials, involving metals, such as copper with a small percentage of ametal, such as bismuth. Consider, for example, patents of the type suchas Lafferty U.S. Pat. No. 2,975,255 and Lafferty et al. U.S. Pat. No.3,246,979 as examples of such patents.

The materials covered by the aforesaid patents have a very lowmechanical strength, and, thereby, do not have as severe a weld problem.Another partial solution to the weld problem is to choose metals, orcombinations of metals, which produce brittle materials at the electrodeinterface. In general, the approach to the problem of contact weldinghas been to choose specific metals or combinations of metals, which aremechanically weak, or which produce weak or brittle materials at thereacted interface between the separable contacts.

A disadvantage arises from contact surfaces, which have a low mechanicalstrength. Lower mechanical strength generally connotes a depressed highvoltage withstand" ability. Also, lower mechanical strength materialsare more prone to erosion.

SUMMARY OF THE INVENTION According to a preferred embodiment of thepresent invention, a pair of separable contacts are provided for avacuumtype circuit interrupter in which the contact arrangement isasymmetrically arranged. The line'of contact engagement is deliberatelyprovided at an appreciable distance from the line of action of theforces tending to separate the contacts, so that a bending moment occurswhich aids in weld breaking. The weld breaking moment is a function ofthe force pulling the contacts apart and the radius from the line ofaction of the force to the center of the welded area. A minutecounterrotation of the electrodes is required to accomplish the tearingaction.

Accordingly, it is a general object of the present invention to providean improved separable-contact arrangement for vacuumtype circuitinterrupters in which an asymmetrical arrangement is provided to providea bending moment at the time of contact separation and resultant circuitinterruption.

A more specific object of the present invention is the provision of animproved vacuum-type circuit interrupter of low welding characteristics.

Still a further object of the present invention is the provision of animproved weld-free vacuum-type circuit interrupter in which a minimum oftensile forces may be required to accomplish the opening operation.

Still a further object of the present invention is the provision of avacuum-type circuit interrupter of reduced welding characteristicsprovided by a lateral displacement of the line of action of theweld-breaking area from the line of action of the tensile forces,induced by operation of the operating rod in its longitudinal openingmovement.

Further objects and advantages will readily become apparent upon readingthe following specification taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a vertical sectional viewtaken longitudinally through a vacuum-type circuit interrupter showing aseparable contact arrangement employing the principles of the presentinvention, the contacts being shown in the fully open-circuit position;and,

FIG. 2 is a fragmentary view of the contact structure of FIG. 1 at thetime of initial contact separation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, andmore particularly to FIG. 1 thereof, the reference numeral 1 generallydesignates a vacuum-type circuit interrupter. As shown, the vacuum-typecircuit interrupter 1 comprises a highly evacuated envelope 2 comprisinga tubular insulating casing, formed of glass or a suitable ceramicmaterial. Sealed to the ends of the tubular insulating casing 2 is apair of end plates, or caps 3, 4, which are sealed in a vacuum-typemanner to the ends of the tubular casing 2 as at 3a, 4a. This may beaccomplished in a manner well known by those skilled in the art.

The normal pressure within the envelope is lower than l0 mm. of mercury,so that a reasonable assurance is had that the mean free path forelectrons will be longer than the potential breakdown paths within theenvelope.

Located within the envelope is a pair of relatively separable contactsor electrodes 5, 6, which are shown in FIG. 1 in their separated oropen-circuit position. One of the contacts or electrodes 5 is astationary contact of generally disc-shape, whereas the other separablecontact 6 is a movable contact also in the shape of a round disc. Whenthe circuit interrupter is in its closed position, the movable contact 6engages the stationary contact 5 in a manner generally indicated in FIG.2 of the drawing. In the closed position, current may flow from the lineterminals L,, L,.

The movable contact 6 is suitably joined to the end of a conductiveoperating rod 8. The operating rod 8 projects through an opening 9provided in the end cap 4, and a flexible metallic bellows 12 provides aseal about the operating rod 8 to allow for the longitudinal operatingmovement of the rod without impairing the vacuum inside the envelope 2.As shown in FIG. 1, the metallic bellows is secured in sealedrelationship at its respective opposite ends to the operating rod 8 andalso to the end cap 4.

The stationary contact 5 is mounted upon a conductor 14 of highconductivity material, such as copper. This conductor has an extensionat its outer end, that extends through the end cap 3 and serves as oneterminal for the vacuum-type circuit interrupter 1. A suitable brazedjoint is provided about the extension to maintain the envelopevacuum-tight, and to provide a mechanically strong connection betweenthe end cap 3 and the extension.

As stated hereinbefore, one of the problems in the interruption ofvacuum-type circuit interrupters is the welding problem, which must beovercome. All of the vacuum circuit interrupter designs known to me havethe electrode stems and contact surfaces geometrically arranged so thatthe welds, which are formed between the contacts, must be broken byalmost pure tension. In other words, the lines of action of the forces,used to pull the contacts apart, are concurrent with the center of thecontact area. I propose in my invention that the center of the contactsurface area of the electrodes, or contacts be displaced from the lineof action of the forces used to separate the contacts. As a result, thewelds will be more easily broken because of the combined action oftension and bending, which will produce a localized high stress in theweld, and, thereby, result in a tearing action. By applying thesuggested concept, it will be possible to use materials which wouldotherwise be prohibited because of welding. Generally, it is mostdesirable to provide an asymmetrical arrangement, as shown in FIGS. 1and 2. FIG. 1 shows a generally simple form of the invention whichutilizes the proposed concept. The bending moment, which aids in weldbreaking, is a function of Fr, I

where F is the force pulling the contacts apart, and r is the radiusfrom the line of action of the force to the center of the welded area.It is obvious that a minute counterrotation of the electrodes isrequired to accomplish the tearing action. This is more clearlyillustrated in FIG. 2 of the drawings, which shows the initial time ofcontact separation with the tearing or bending action illustrated andangle indicating such bending action.

It is to be clearly understood that the proposed asymmetricalarrangement may be used in combination with other types of contactconfiguration, involving slots or spirals, or any other type of contactarrangement. In effect, it may be superimposed upon the proposed contactarrangement to provide the desired offcenter, or asymmetrical bendingmoment to more clearly break the weld.

Although there has been illustrated and described a specific structure,it is to be clearly understood that the same was merely for the purposeof illustration, and that changes and modifications may readily be madeby those skilled in the art without departing from the spirit and scopeof the invention.

I claim as my invention:

1. A circuit interrupter of the vacuum-type comprising:

a. a first electrode;

b. support means for the first electrode;

0. a second electrode making physical contact with the first electrodeduring the closing stroke of the interrupter and thereby defining anintercontact weld-breaking area;

d. the second electrode separable from the first electrode to establishan arc;

e. means defining an evacuated envelope surrounding said separableelectrodes;

f. operating-rod means for effecting a separation of said separableelectrodes; and,

g. the line of action of the weld-breaking area being displaced from theline of action of the operating-rod means and also the line of action ofthe said support means, whereby a bending moment is produced forfacilitating the breaking of the weld during the opening operation.

2. The circuit interrupter of claim I in which the two separableelectrodes and their supporting portions form a laterally bowed currentpath through the interrupter displaced from the axis of the interrupter.

3. The circuit interrupter of claim I in which the electrodes aredisc-shaped and the supporting contact stems constitute offset portions.

4. A circuit interrupter of the vacuum-type comprising:

a. a stationary contact;

b. support rod means for the stationary contact;

c. a movable contact separable from the stationary contact to establishan are;

d. means defining an evacuated envelope surrounding said separablecontacts;

e. and means including the location of the contact area between thestationary and movable contacts laterally of the line of action of saidsupport rod means for creating a bending movement upon the contactportions during the opening operation to facilitate the breaking of thewelds which occur during the opening operation.

5. The circuit interrupter of claim 4, wherein the contacts aredisc-shaped and the supporting contact stem portions are laterallyoffset from the central axis of the circuit interrupter.

1. A circuit interrupter of the vacuum-type comprising: a. a firstelectrode; b. support means for the first electrode; c. a secondelectrode making physical contact with the first electrode during theclosing stroke of the interrupter and thereby defining an intercontactweld-breaking area; d. the second electrode separable from the firstelectrode to establish an arc; e. means defining an evacuated envelopesurrounding said separable electrodes; f. operating-rod means foreffecting a separation of said separable electrodes; and, g. the line ofaction of the weld-breaking area being displaced from the line of actionof the operating-rod means and also the line of action of the saidsupport means, whereby a bending moment is produced for facilitating thebreaking of the weld during the opening operation.
 2. The circuitinterrupter of claim 1 in which the two separable electrodes and theirsupporting portions form a laterally bowed current path through theinterrupter displaced from the axis of the interrupter.
 3. The circuitinterrupter of claim 1 in which the electrodes are disc-shaped and thesupporting contact stems constitute offset portions.
 4. A circuitinterrupter of the vacuum-type comprising: a. a stationary contact; b.support rod means for the stationary contact; c. a movable contactseparable from the stationary contact to establish an arc; d. meansdefining an evacuated envelope surrounding said separable contacts; e.and means including the location of the contact area between thestationary and movable contacts laterally of the line of action of saidsupport rod means for creating a bending movement upon the contactportions during the opening operation to facilitate the breaking of thewelds which occur during the opening operation.
 5. The circuitinterrupter of claim 4, wherein the contacts are disc-shaped and thesupporting contact stem portions are laterally offset from the centralaxis of the circuit interrupter.